chore: publish from main

2026-08-17 14:46:56 +00:00 · 2026-08-11 02:48:20 +00:00
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+# Oracle to PostgreSQL: Date Functions, Sequences, and DUAL
+
+## Problem
+
+Oracle relies on several built-in constructs — `SYSDATE`, `SYSTIMESTAMP`, sequence `NEXTVAL` syntax, and the `DUAL` dummy table — that do not exist in PostgreSQL. Each requires a direct substitution.
+
+## SYSDATE and SYSTIMESTAMP
+
+**Oracle:**
+- `SYSDATE` — returns the current date and time (no time zone) as an Oracle `DATE` type
+- `SYSTIMESTAMP` — returns the current timestamp with time zone
+
+**PostgreSQL:**
+- Use `NOW()` or `CURRENT_TIMESTAMP` for timestamp with time zone
+- Use `CURRENT_DATE` for date only
+- Use `LOCALTIMESTAMP` for timestamp without time zone (closer to Oracle's `SYSDATE` semantics)
+
+```sql
+-- Oracle
+SELECT SYSDATE FROM DUAL;
+INSERT INTO t (created_at) VALUES (SYSDATE);
+
+-- PostgreSQL
+SELECT NOW();
+INSERT INTO t (created_at) VALUES (NOW());
+-- or, if the column is DATE-only:
+INSERT INTO t (created_at) VALUES (CURRENT_DATE);
+```
+
+> **Warning:** Oracle `DATE` stores date *and* time; PostgreSQL `DATE` stores date only. If Oracle columns typed as `DATE` carry a time component, the PostgreSQL target column should be `TIMESTAMP`, not `DATE`.
+
+## Sequence NEXTVAL Syntax
+
+**Oracle:**
+```sql
+SELECT my_sequence.NEXTVAL FROM DUAL;
+INSERT INTO t (id) VALUES (my_sequence.NEXTVAL);
+```
+
+**PostgreSQL:**
+```sql
+SELECT nextval('my_sequence');
+INSERT INTO t (id) VALUES (nextval('my_sequence'));
+```
+
+Key differences:
+- PostgreSQL `nextval()` is a function call with the sequence name as a quoted string argument
+- Oracle uses dot notation: `sequence_name.NEXTVAL`
+- Oracle also has `CURRVAL` → PostgreSQL `currval('sequence_name')`
+- If the column uses a `DEFAULT nextval(...)` constraint (set during Phase 4 DDL migration), application code can omit the sequence call entirely and omit the column from the `INSERT`
+
+## DUAL Table
+
+Oracle requires a `FROM DUAL` clause in `SELECT` statements that evaluate expressions without a real table. PostgreSQL does not have `DUAL` — expressions can be selected without a `FROM` clause.
+
+```sql
+-- Oracle
+SELECT 1 + 1 FROM DUAL;
+SELECT SYSDATE FROM DUAL;
+SELECT my_sequence.NEXTVAL FROM DUAL;
+
+-- PostgreSQL
+SELECT 1 + 1;
+SELECT NOW();
+SELECT nextval('my_sequence');
+```
+
+> **orafce extension:** If `orafce` is installed, it provides a `DUAL` view that makes Oracle-style `FROM DUAL` queries work without changes. This is a useful transitional aid but should not be relied on permanently.
+
+## Migration Actions
+
+### 1. Stored Procedures
+
+- Replace all `SYSDATE` / `SYSTIMESTAMP` references with `NOW()` or `CURRENT_TIMESTAMP` (verify column type — use `LOCALTIMESTAMP` if the target is `TIMESTAMP WITHOUT TIME ZONE`)
+- Replace `sequence_name.NEXTVAL` with `nextval('sequence_name')`
+- Replace `sequence_name.CURRVAL` with `currval('sequence_name')`
+- Remove `FROM DUAL` from all expression-only `SELECT` statements
+
+### 2. Application Code (inline SQL strings)
+
+Search C# string literals for `SYSDATE`, `SYSTIMESTAMP`, `.NEXTVAL`, `.CURRVAL`, and `FROM DUAL`. Apply the same substitutions.
+
+### 3. Tests
+
+- Verify datetime assertions use timezone-safe comparisons (see `oracle-to-postgres-timestamp-timezone.md` for Npgsql-specific behavior)
+- Verify sequence-dependent IDs are correctly populated in assertions